The purpose of the proposed research is to establish a rapid, inexpensive, in vitro system for studying the cytotoxicity and genotoxicity of particulates potentially hazardous to the respiratory system. Short term tests currently available to the research community were designed and optimized using soluble test materials and have been adapted to the study of particulates with limited phagocytic capacity of the target cells. The proposed assay system would use a functional mouse macrophage cell line. This cell line, RAW264.7, is avidly phagocytic, can undergo a respiratory burst, and grows readily in culture. This latter feature will allow both cytotoxicity and genotoxicity end points to be measured. Phase I goals will be to 1) establish the optimal conditions for a cytotoxicity assay, 2) validate the cytotoxicity assay with known toxic particulates, 3) establish the assay conditions for an HGPRT based forward mutation assay, and 4) assay several known classes of mutagenic particulates.